Abstract: A power switching circuit is connected to an external power source, a battery, and a load. The power switching circuit includes a voltage converter, a prevention unit, a detecting unit, and a switch. The voltage converter converts a first primary voltage supplied by the external power source to a secondary voltage. The prevention unit allows the secondary voltage to be transmitted to the load, the secondary voltage powering the load. The detecting unit generates a first level signal when the external power source fails to output the first primary voltage. The switch is turned on to transmit a second primary voltage supplied by the battery to the load and the prevention unit in response to the first level signal. The second primary voltage powers the load. The prevention unit prevents the second primary voltage from being transmitted to the voltage converter.